Design of the front-end system of the hottest mill

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Millimeter wave radar front-end system design

1 introduction

the working frequency of millimeter wave is between microwave and light. Compared with microwave mine, "light pressure" of millimeter wave radar is the light emitted on the object. The pressure produced by millimeter wave radar is small, light, narrow wave speed, large bandwidth and strong anti-jamming ability; It has better weather adaptability than infrared or laser sensors, so it is a rising star in the use of electromagnetic spectrum after laser and infrared. In the past, the application of millimeter wave radar was limited by the low power of devices, especially active devices, which made it difficult to play a role in the field of design specification for Halon 1211 fire extinguishing system beyond terminal guidance gbj110 (87). However, this is not what it used to be. After a major breakthrough was made in the planning of microwave and millimeter wave integrated circuits in the second stage of the 1990s, high-power millimeter wave power sources, dielectric antennas, integrated antennas, low-noise receiver chips, etc. have been introduced one after another, which has led to an update of millimeter wave radar and greatly broadened its application fields

2 millimeter wave radar front-end system design principle

high measurement accuracy and range resolution are obtained by using the good autocorrelation characteristics of pseudo-random coded signals and low range sidelobes. At the same time, the echo signal power of sine wave FM signal system is used as the distance function to effectively suppress the near-field clutter interference. Figure 1 is a block diagram of a composite modulation system using two continuous wave signals: pseudo-random coded phase modulation and sine wave frequency modulation


16 GHz high frequency oscillator generates 16 GHz 10 MHz microwave oscillation signal, which is sinusoidally modulated and sent to the phase modulator for random coding phase modulation. The phase modulated signal passes through the power divider, part of which is amplified and radiated by the transmitting antenna, and the other part of the leakage signal is added to the signal mixer. After the RF signal radiated by the antenna irradiates the target, the echo signal reflected by the target is received by the antenna, and the echo signal is sent to the signal mixer to mix with the leakage signal and filter out the high-frequency signal to obtain the video signal. The amplified video signal can be sent to the headset after digital signal processing, so as to directly monitor the movement, speed and state of the target

as shown in Figure 1, the main components of the radar front-end system include oscillator, 0/phase modulator, power amplifier and mixer

2.1 dielectric oscillator

the dielectric oscillator adopts the GaAs FET dielectric feedback oscillator as shown in Figure 2. GaAs FET dielectric feedback oscillator can adopt drain output or source output. In order to obtain the maximum output power, the form of drain output and source direct grounding is selected

the commonly used dielectric oscillator modes are TE01 mode, TM01 mode and HE11 mode, but when coupled with microstrip, TE01 mode is generally selected, because its electromagnetic field is circularly symmetrical, it is very convenient to couple with microstrip, and the oscillation mode is stable. In this paper, cylindrical dielectric resonator is selected, with diameter d=3.423 mm and height h=2.28 mm. Parameters: f=16 GHz, r=40. In the actual circuit, the mechanical/foaming/thermal/electrical properties of ABS/graphite thin nanocomposites prepared by micro foaming injection molding and injection compression molding are applied to the resonator and microstrip. A dielectric sheet with low dielectric constant and low loss is placed between the substrates to reduce the influence of the microstrip substrate and metal ground plate on the Q value and temperature performance of the resonator

2.20/phase modulator

0/phase modulator adopts switch line phase modulator. The electrical schematic diagram of the phasor in recent years is shown in Figure 3. L1 and L2 are two microstrip transmission lines with different lengths (or any other microwave transmission line) , D1, D2, D3 and D4 are four pin diodes with consistent performance. When the diodes on both sides are complementary and biased, when diodes D1 and D2 are on, D3 and D4 are in the cut-off state, and the carrier frequency signal is transmitted through L1. On the contrary, when D1 and D2 are cut off, D3 and D4 are in the on state, and the carrier frequency signal is transmitted through L2. Obviously, due to the different lengths of L1 and L2, phase shift effect is caused

set the shorter path as L1 and the longer path as L2. Then the phase modulation phase is:

2.3 power amplifier

as shown in Figure 1, the dielectric oscillator generates a 16 GHz 10 MHz oscillation signal of 6 ~ 9 DBM. In order to ensure that the signal can be transmitted, the minimum value is taken for design. The signal of 6 DBM passes through the isolator loss of 1 DBM, and then passes through the 0/phase modulator loss of 1 DBM to obtain a signal of 4 DBM. After the 4 DBM signal passes through the 3 DBM power divider, only 1 DBM of the signal enters the power amplifier. To obtain the 17 DBM transmission signal, the power amplifier must amplify at least about 18 DBM. By selecting the appropriate amplifier tube and designing a certain amplifier circuit, the performance index required by the design can be achieved finally

2.4 signal mixer

the signal mixer adopts the double balanced mixer as shown in Figure 4

the characteristic of this circuit is that the local oscillator and signal voltage are respectively added to the diode through the balanced unbalanced converter. This converter is called balun for short, and the balun is used to replace the directional coupler and high and low frequency short line, which widens the working frequency band. The signal and local oscillator power are respectively added to the two diagonals of the diode bridge through balun. As long as the four diodes have the same performance and the bridge is balanced, the signal can be completely isolated from the lo port. At the same time, the diode bridge provides high and low frequency and DC channels for the diode

this mixer has the following advantages: high isolation of double balanced mixer; Large dynamic range; The double balanced mixer is a broadband mixer

3 conclusion

after a long time of research, a millimeter wave radar front-end system has been developed to meet the requirements. The system adopts the design schematic diagram of millimeter wave radar front-end system as shown in Figure 1. The working frequency is 16 GHz, the frequency offset is less than or equal to 10 MHz at room temperature, the output power is po 45 MW, and the phase noise is -70 DBC/Hz/10 kHz. 0/the carrier suppression of phase modulator at room temperature is -25 DB under 750 kHz symmetrical square wave

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